As is known, nappies comprise an impermeable layer, for example of polyethylene, a layer of non-woven fabric permeable to liquids and an absorbent pad sandwiched therebetween.
Absorbent pads are made mainly from natural fibre material (known as “fluff”) uniformly blended with superabsorbent polymer material (“SAP”).
In order to increase pad absorption capacity absorbent pads have been developed which comprise one or more discrete absorbent layers made mainly from superabsorbent polymer material (“SAP”).
It is known from the prior art that a unit for making absorbent pads for nappies comprises a drum, which rotates about its axis of rotation and which has on its peripheral cylindrical surface a plurality of suction housings or recesses within which respective absorbent pads are formed.
The unit also comprises a hood which is used for feeding fluff mixed with “SAP” and which is located to face the peripheral cylindrical surface of the drum.
The fluff and “SAP” are fed pneumatically into the hood and, once mixed, settle in the suction recesses formed on the drum and located to face the hood.
It is also known that the unit comprises a feeding duct having a mouth for delivering charges of superabsorbent material (“SAP”) used to define the above mentioned discrete absorbent layers.
Intermittent valve means regulate the feed flow of the feeding duct as a function of the spacing of the drum recesses, so that discrete charges of superabsorbent polymer material (“SAP”) are delivered exactly at the moment a suction recess of the drum comes to face the delivery mouth of the duct itself.
It has been found, however, that on account of incorrect manual settings or mechanical malfunctions, the intermittent valve means go out of phase with the rotation of the drum and, consequently, the feeding duct does not deliver the discrete charges of superabsorbent polymer material when a suction recess only partly faces the duct delivery mouth or does not face the duct delivery mouth.
This leads to the formation of defective absorbent pads because the discrete layers of superabsorbent polymer material in the respective pad are not positioned correctly relative to a reference position.
The incorrect position of the discrete layers of superabsorbent polymer material reduces the effective liquid absorbing capacity of the absorbent pad.